This is a form of validation for Twitter and other short message services. Twitter is taking a bite out of the Telco SMS market. Where the cost of a tweet is a fraction of the cost of an SMS.
So just like the internet VoIP took a bite from Telco IDD revenues, Tweeting services are taking a bite of SMS revenues. Although this is substantially a smaller loss of revenue for Telcos, Telcos are still in charge controlling the use of phone-based bandwidth.
So VoIP, SMS, and other social phone applications are leading the charge to a data driven phone network. Nothing really new. But the evolution is being validated.